1. Field of the Invention
The present invention relates to a laser diode driving circuit having a temperature compensation circuit for keeping an optical output constant relative to the change of temperature.
2. Prior Art
FIG. 2 shows a conventional laser diode driving circuit having a temperature compensation circuit. Denoted at 1 is a laser diode (hereinafter referred to as an LD), 2 is a transistor (hereinafter referred to as a TR) for driving the LD 1, 6 is a photodiode, 7 is a differential amplifier, 8 is a reference power supply and 9 is a monitor light.
The monitor light 9 emitted by the LD 1 is detected by the photodiode 6 and the output power of the monitor light 9 is converted into an electric signal the magnitude of which is compared by the differential amplifier 7 with a reference voltage of the reference power supply 8 which is set beforehand at a certain temperature wherein the result of comparison is fed back to the TR 2 so as to control the output current of the TR 2 whereby the optical output from the LDI is kept constant. In FIG. 2, a feedback circuit is formed of the LD 1, the photodiode 6, the differential amplifier 7, the TR 2 and the LD 1.